1. Field of the Invention
The present invention relates to a process and a plant for building tyres.
In greater detail, the invention concerns the process and the equipment used for building the green tyre, to be subsequently submitted to a curing cycle for obtaining the final product.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”, having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers, placed in radial superposed relationship on each other and on the carcass ply, having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band is applied at a radially external position to the belt structure, which tread band too is made of elastomeric material like other semifinished products constituting the tyre.
In addition respective sidewalls of elastomeric material are applied at an axially external position onto the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the “tubeless” type, an air-tight coating layer, usually referred to as “liner” covers the inner tyre surfaces.
The carcass structure and belt structure are generally made separately from each other in respective work stations, to be then mutually assembled.
After building of the green tyre carried out through assembly of respective components, a curing and molding treatment is generally carried out which aims at determining the structural stabilisation of the tyre through cross-linking of the elastomeric compounds and impressing the same with a desired tread pattern and possible distinctive graphic marks at the tyre sidewalls.
Known are production processes in which, as disclosed in WO 01/36185 for example, in the name of the same Applicant, the structural tyre elements are manufactured on a suitably-shaped toroidal forming support, by sequentially laying a plurality of elementary components thereon, which components for example consist of rubberised individual cords or cords cut to size parallelly gathered in the form of strip-like elements, particularly used in making the carcass and belt structures, and continuous elongated elements of elastomeric material, particularly used for making other structural elements of the tyre such as tread band, sidewalls, liner, fillers, auxiliary support inserts, for example.
According to the aforesaid document WO 01/36185 and document WO 00/35666, in the name of the same Applicant as well, the elementary components are applied to, and suitably distributed on the forming support while the latter is being supported in overhanging at a shank coaxially projecting from the forming support through a robotized arm. The robotized arm sets the toroidal support in rotation around its axis and suitably moves it in front of an extruder or other dispensing device for determining the controlled distribution of the elementary components, based on a predetermined deposition schedule pre-set on a computer.
WO 2009/040594 in the name of the same Applicant, discloses a plant and a process for producing tyres comprising the following steps: a) forming a carcass structure of a green tyre on a first building drum in at least one carcass-building line; b) forming a crown structure on an auxiliary drum, in at least one crown structure-building line; c) shaping the carcass structure into a toroidal conformation so as to couple it to the crown structure in at least one assembling and shaping station for the tyre being processed. Operation of the assembling and shaping station is synchronised with that of the carcass-building line and the crown structure-building line. Each carcass structure remains in engagement on the respective building drum at least until completion of the shaping step. The built tyre is molded and cured in a curing and molding line separated from the assembling and shaping station. Robotized arms carry out transfer of the building drums from the carcass-building line to the assembling and shaping station, as well as transfer of the auxiliary drums from the crown structure-building line to the assembling and shaping station, and also between the different work stations provided along the crown structure-building line.
WO 2009/128046 also in the name of the same Applicant, describes a plant comprising an assembling station in which a carcass sleeve and an outer sleeve previously manufactured in respective building lines, are mutually coupled. Integrated into the assembling station are engagement devices that can be alternately coupled to an auxiliary drum carrying an outer sleeve previously formed in the crown structure-building line, and to a building drum carrying a carcass sleeve formed in the carcass-building line.
These engagement devices comprise a powered chuck and a footstock designed to engage a first and a second end respectively of a drum-supporting shaft, projecting on opposite sides from the respective building drum/auxiliary drum.
The outer sleeve is picked up from the auxiliary drum previously associated with the engagement devices, to be then coupled to the carcass sleeve carried by the building drum associated with the respective engagement devices in place of the auxiliary drum.
A robotized arm carrying a fork-shaped end portion carries out transfer of the building drum from the carcass-building line to the engagement devices provided in the assembling station.